1. Field of the Invention
The invention relates to rotating unions such as are used in loading fluids from manufacturing or storing facilities into railroad tank cars, tank trucks and the like. Such unions are referred to in the trade as swivel joints and must be leak proof as well as being fully rotatable to adjust for a variety of loading operations.
2. Prior Art
Rotating unions of swivel joints as they are often referred to are used for loading fluids from storage or manufacturing facilities to railroad tank cars, tank trucks, tanker ships and the like. A serious problem with the prior art units has been that they take a good deal of time to disassemble and reassemble when the packing used therein needs replacement. Thus, it often takes over one and one-half hours to replace worn packing rings in the most common existing swivel joint units. Such swivel joint units generally have machined ball-bearing raceways as an integral part of an outer cylindrical member and of an inner cylindrical member. Grease laden balls are individually removed via a typical small threaded port plug which is itself part of the raceway. Since the port plug is part of the raceway it is itself subjected to radial loading. Also, the axial thrust raceway arc creates a circumferential discontinuity at the ball loading ports. The ball loading ports are normally made as small as possible to minimize the arc of the circumferential raceway discontinuity thus making loading of clean balls difficult and the removal of grease laden balls quite arduous, and, since there are usually well over fifty balls present, quite time consuming also. Further, machining imperfections and/or grains of sand or other abrasive materials in the threads of the port plug can cause improper seating thereof so that every ball rolling over the discontinuity during operational swivel rotation is subjected to potential surface damage.
Because the ball-bearing raceways of the most common existing units are machined into the outer tube and the inner tube, the raceways must be hardened; but, this creates brittle portions thereof and introduces potential metal thermal stress problems.
still another problem with the prior art designs of this nature is that the two ball-bearing raceways which are machined into the inner and outer tubes and are spaced from one another must both be capable of bearing both high axial thrust and high radial thrust. Yet, when such swivels are used to transport liquids and are attached to heavy lengthy pipes where the swivel must support a load with a high bending moment at the rotating swivel with liquid flowing through at little or no pressure, a high radial load bearing is desirable but only low axial load capabilities are needed. Equally frequently, however, a swivel may be required to transport a high pressure liquid in a system with little or no bending moment. In such a use high axial thrust bearing having a low radial load is best suited. Existing commercial swivels cannot offer this versatility and instead make use of a pair of ball-bearing units spaced apart from one another, each of which is capable of both high axial thrust bearing and high radial thrust bearing.
Another problem yet with prior art swivel joints is that uniform compression of the packing to cause the packing to radially expand into sealing relation with the inner and outer tubes is not usually adequately attained. The prior art devices generally use a plurality of small coil springs equally spaced about the inner tube and compressing the packing axially between the inner tube and the outer tube. Besides providing insufficiently uniform distribution of the compression, such individual coil springs do not generally provide as great a compression as is desirable in certain operations. Still further, removal and replacement of a number of tiny coil springs is difficult and time consuming. Yet further, the packing often rotates relative to the coil springs in existing swivels. This action destroys the axial coil spring alignment or breaks or damages the coil springs so severely they become non-functional.
Rotary fluid joints have been designed which utilize a pair of ball-bearing units which are held in place by snap rings or the like whereby some of the above-mentioned problems are solved. Such units are disclosed for example in U.S. Pat. No. 2,723,136 and in U.S. Pat. No. 3,889,983. However, in such prior art rotary fluid joints each of the ball-bearing units has borne both a radial and an axial load with axial load being transferred from one ball-bearing unit to the next. Further, the prior art units of this nature have not been such as to exert pressure uniformly upon packing material, and, indeed, the sealing elements utilized have generally not been compressed between either of the ball-bearing assemblies and the tubes entering the union. Thus, the prior art has not provided an apparatus wherein especially useful and low friction bearing units can be used independently for axial and radial loading or wherein the tension upon the packing can be easily adjusted or wherein the packing is compressed between the outer tube and an outer race of the bearing structure nearest the end of the inner tube.